The performance of a vehicle is limited, in part, by the level of traction between tires of the vehicle and the road surface on which the vehicle travels. All other parameters being equal, with more traction, a vehicle can accelerate, change direction, and stop more quickly. Traction between the tires and the road surface is directly proportional to the friction between the tires and the road surface, which, in turn, is directly proportional to the coefficient of friction between the tires and the road surface. The coefficient of friction is largely a function of characteristics of the material and tread of the tires and characteristics of the road surface, such as, for example, the material and texture of the road surface and any coating on the road surface, such as, for example, dirt, oil, water, snow, or ice.
As a result, the vehicle may lose control during acceleration, steering, and/or braking inputs that result in the vehicle tires losing traction with the road surface, particularly when the road surface has a coating of water, snow, or ice. In addition, for a typical autonomously controlled vehicle, the vehicle has no ability to estimate the friction or level of traction between the tires and the road surface on which the vehicle travels based on the characteristics of the surface. As a result, an autonomously controlled vehicle may attempt maneuvers that require more traction than is available for the given road surface, which may result in the vehicle losing control. Alternatively, the autonomously controlled vehicle may be programmed to make maneuvers at acceleration, turning, and/or braking rates slow enough to ensure that traction limitations are not exceeded, regardless of the level of traction available between the tires and the surface. This may result in an undesirably low level of maneuvering performance, particularly if the vehicle is programmed to operate on road surfaces coated with water, snow, or ice. As a result, an autonomously controlled vehicle programmed to operate in this manner may maneuver at an undesirably slow rate in many conditions.